This application is based on Application No. 2000-007925, filed in Japan on Jan. 16, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an automotive alternator and particularly to a positional relationship between a cooling fan and a stator winding.
2. Description of the Related Art
FIG. 10 is a cross section showing a conventional automotive alternator.
In FIG. 10, the automotive alternator includes: a case 3 constituted by an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 disposed inside the case 3 having a pulley 4 secured to a first end thereof; a Lundell-type rotor 7 secured to the shaft 6; front-end and rear-end centrifugal fans 5 functioning as cooling fans secured to front and rear axial end surfaces of the rotor 7; a stator 8 secured to the case 3 so as to envelop the rotor 7; slip rings 9 secured to a second end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 sliding on surfaces of the slip rings 9; a brush holder 11 accommodating the brushes 10; a rectifier 12 electrically connected to the stator 8 for converting alternating current generated in the stator 8 into direct current; and a regulator 18 mounted to a regulator heat sink 17 fitted onto the brush holder 11, the regulator 18 adjusting the magnitude of an alternating voltage generated in the stator 8.
The rotor 7 is constituted by a field winding 13 for generating a magnetic flux on passage of an electric current, and a pair of first and second pole cores 20 and 21 disposed so as to cover the field winding 13, magnetic poles being formed in the first and second pole cores 20 and 21 by magnetic flux generated in the field winding 13. The pair of first and second pole cores 20 and 21 are made of iron, each has a plurality of first and second claw-shaped magnetic poles 22 and 23 having a generally trapezoidal outermost diameter surface shape disposed on an outer circumferential edge portion at even angular pitch in a circumferential direction so as to project axially, and the first and second pole cores 20 and 21 are fixed to the shaft 6 facing each other such that the first and second claw-shaped magnetic poles 22 and 23 intermesh.
The stator 8 is constituted by: a cylindrical stator core 15 formed by laminating a magnetic steel plate; and a stator winding 16 installed in the stator core 15. The stator 8 is held between the front bracket 1 and the rear bracket 2 so as to form a uniform air gap between outer circumferential surfaces of the claw-shaped magnetic poles 22 and 23 and an inner circumferential surface of the stator core 15.
The rectifier 12 is constituted by: unidirectional conducting component packages 24 for three-phase full-wave rectification of output from the stator winding 16; a pair of rectifier heat sinks 25; and a circuit board 26 in which wiring constituting a bridge circuit is insert molded. The unidirectional conducting component packages 24 are each formed into a generally rectangular parallelepiped shape by molding a diode 24a joined to a heat-dissipating tab 24b into an electrically-insulating resin portion 24c. A predetermined number of the unidirectional conducting component packages 24 are mounted to each of the rectifier heat sinks 25 by joining the heat-dissipating tabs 24b to a main surface of each of the rectifier heat sinks 25.
In an automotive alternator constructed in this manner, an electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the field winding 13, generating a magnetic flux. The first claw-shaped magnetic poles 22 on the first pole core 20 are magnetized into North-seeking (N) poles by this magnetic flux, and the second claw-shaped magnetic poles 23 on the second pole core 21 are magnetized into South-seeking (S) poles.
At the same time, the pulley 4 is driven by an engine and the rotor 7 is rotated by the shaft 6. A rotating magnetic field is applied to the stator core 15 due to the rotation of the rotor 7, generating an electromotive force in the stator winding 16. The alternating electromotive force generated in the stator winding 16 is converted into direct current by the rectifier 12 and the magnitude of the voltage output therefrom is adjusted by the regulator 18, recharging the battery.
Now, the field winding 13, the stator winding 16, the rectifier 12, and the regulator 18 continuously generate heat during power generation, and in an automotive alternator having a rated output current in the 100A class, the amount of heat generated at rotational frequencies at which the temperature is high is 60W, 500W, 120W, and 6W, respectively.
Thus, in order to cool the heat generated by power generation, front-end and rear-end air intake apertures 1a and 2a are disposed through axial end surfaces of the front bracket 1 and the rear bracket 2, and front-end and rear-end air discharge apertures 1b and 2b are disposed through radial side surfaces of the front bracket 1 and the rear bracket 2 so as to face coil end groups 16f and 16r of the stator winding 16.
Thus, the centrifugal fans 5 are rotated and driven together with the rotation of the rotor 7, and front-end and rear-end cooling airflow channels are formed in which external air is sucked inside the case 3 through the front-end and rear-end air intake apertures 1a and 2a, flows axially towards the rotor 7, is then deflected centrifugally by the centrifugal fans 5, thereafter crosses the coil end groups 16f and 16r, and is discharged outside through the front-end and rear-end air discharge apertures 1b and 2b. A rotor cooling airflow channel is also formed in which a cooling airflow flows through the inside of the rotor 7 from a front end to a rear end as a result of a pressure difference between the front end and the rear end of the rotor 7.
As a result, heat generated in the stator winding 16 is dissipated from the coil end groups 16f and 16r to the front-end and rear-end cooling airflows, suppressing temperature increases in the stator 8. Furthermore, heat generated in the diodes 24a and the regulator 18 is dissipated to the rear-end cooling airflow through the rectifier heat sinks 25 and the regulator heat sink 17, suppressing temperature increases in the rectifier 12 and the regulator 18. In addition, heat generated in the field winding 13 is dissipated to the rotor cooling airflow flowing through the rotor 7, thereby suppressing temperature increases in the rotor 7.
In the automotive alternator constructed in this manner, heat-generating parts such as the stator 8, the rectifier 12, etc., are cooled by the cooling airflows flowing through the cooling airflow channels formed by the centrifugal fans 5.
Here, inflow flow rates of the cooling airflows flowing through the cooling airflow channels depend on ventilation resistance in the cooling airflow channels, the inflow flow rates decreasing as ventilation resistance increases. This decrease in the inflow flow rates of the cooling airflows causes a decrease in cooling of the rectifier 12 and the regulator 18. Furthermore, an amount of overlap between the front-end centrifugal fan 5 and the front-end coil end group 16f and between the rear-end centrifugal fan 5 and the rear-end coil end group 16r (an axial length of radial overlap between the two in each case) is one of the factors increasing ventilation resistance in the cooling airflow channels. In other words, if the amount of overlap increases, ventilation resistance increases. Cooling of the stator winding 16 is raised as the amount of overlap increases.
Thus, increasing the amount of overlap between the front-end centrifugal fan 5 and the front-end coil end group 16f and between the rear-end centrifugal fan 5 and the rear-end coil end group 16r leads to improved cooling of the stator winding 16, but causes decreased cooling of the rectifier 12 and the regulator 18.
However, one conventional problem has been that temperatures increase excessively either in the stator winding 16 or in the rectifier 12 and the regulator 18 because the amount of overlap between the front-end centrifugal fan 5 and the front-end coil end group 16f and between the rear-end centrifugal fan 5 and the rear-end coil end group 16r has been set in consideration either of cooling the rectifier 12 and the regulator 18 or of cooling the stator winding 16, but not both.
In view of these conditions, the present applicants have focused on the stator winding 16 and the rectifier 12, both of which are large heat-generating parts, and investigated problems accompanying temperature increases in the stator winding 16 and the rectifier 12.
Excessive increases in the temperature of the stator winding 16 lead to softening of a varnish impregnated in the stator winding 16. As a result, the stator winding 16 rubs against the stator core 15 due to vibration, damaging an electrically-insulating coating on conductor wires of the stator winding 16, thereby decreasing electrical insulation.
Similarly, excessive increases in the temperature of the rectifier 12 cause heat degradation in the diodes 24a of the rectifier 12, shortening the life of the diodes 24a. 
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator enabling the working life of diodes of a rectifier to be extended and deterioration in electrical insulation to be eliminated by setting an amount of overlap between a cooling fan and a coil end group of a stator winding in consideration of a softening temperature of a varnish impregnated into the stator winding and of a heat tolerance threshold of the diodes.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
a shaft rotatably supported by a case;
a rotor fixed to the shaft;
a stator provided with:
a cylindrical stator core supported by the case so as to envelop the rotor, a plurality of slots extending axially being formed in the stator core so as to line up circumferentially; and
a stator winding installed in the stator core;
a rectifier supported by the case so as to face an axial end surface of the rotor; and
at least one cooling fan fixed to at least one axial end surface of the rotor,
wherein the cooling fan is constructed such that a ratio (t/h) between an amount of axial protrusion t of the cooling fan relative to an apex portion of a coil end group of the stator winding and an axial height h of the cooling fan satisfies an expression 0.2 less than t/h less than 0.7.
A gap may be formed between the coil end group of the stator winding and an end surface of the stator core, the gap being positioned closer to an axially-central region than the end surface of the rotor to which the cooling fan is fixed.
Each of winding phase portions constituting the stator winding may be constructed by a divided winding portion.
The cooling fan may be formed so as to have a smaller outside diameter than an outside diameter of the rotor.
An intersecting region between an axial end surface of the rotor and an outer circumferential surface of the rotor may be chamfered.
The cooling fans may be fixed to first and second axial end surfaces of the rotor, the cooling fan fixed to the first axial end surface of the rotor being a centrifugal fan, and the cooling fan fixed to the second axial end surface of the rotor being a mixed-flow fan.
The slots may be disposed at a ratio of two per phase per pole.